Note 98 — MEMOIRS OF THE LIFE OF DAVID RITTENHOUSE; ANTERIOR TO HIS SETTLEMENT IN PHILADELPHIA.

This gentleman’s name is connected with another circumstance in relation to Mr. D. Rittenhouse, which deserves to be noticed. He is in possession of a finely-graduated thermometer, made by our Philosopher; on the scale of which is engraved, by him, the record of a memorable fact concerning the climate of Pennsylvania, referring by a mark to 22° below 0, of Fahrenheit’s scale; viz.—“Jan. 2. 1762—Great Cold in Pennsylvania.” This fact was ascertained by Mr. Rittenhouse, from a reference to the accurate Messrs. Masons and Dixon’s Journal; in which, such was stated to have been the degree of cold in the forks of the Brandywine (about thirty miles westward, and very little to the southward, from Philadelphia,) on the day mentioned.

Mr. Rittenhouse had noticed, that, at his Norriton Observatory, (in lat. 40° 9′ 31″ N.) the mercury in Fahrenheit’s thermometer, not exposed to the sun-shine but open to the air, was at 94½°, on the 5th of July 1769; “which,” says he, “was the greatest height it had ever been observed to rise to, at that place.” But the writer is informed by a judicious and attentive observer, that at Lancaster, Pennsylvania, which is in lat. 40° 2′ 39″ N. (the long. of this borough-town is 5^h 1′ 4″ W. from Greenw.) the mercury rose by Fahrenheit’s scale, on the 7th of July, 1811, to 97½°. Admitting this to be correct, if 1½° be then deducted, for the extra heat of so large a town as Lancaster in comparison with a country-situation, there is in this case the great range of 118° by Fahrenheit’s scale, for the extremes of heat and cold in Pennsylvania.

The writer brought with him, from England, a meteorological diary kept in London, during the severe frost there, from the 7th day of January, 1776, to the 28th of the same month, both days inclusive. The greatest cold, during that period, was 15° and it is thus noted, in respect to the state of the atmosphere at the time; “Clear sky—intense cold—wind west.” The mercury rose on one day, within that time, to 34°. The mean degree of cold, in the same period, was there 26¾°.

The greatest cold at Philadelphia, during the same days of January, 1776, was at 17°, but the mercury rose there, on one of those days, to 48°. The mean degree of cold at Philadelphia, in this corresponding period of time, was 29⅓°; being about 2½° warmer (or rather, less cold,) than the general temperature of the weather in London, at the same time, in what was there called a “severe frost.” Eighty-five degrees of Fahrenheit’s scale is considered as a very extraordinary heat, in London: consequently, a range of 68° may be presumed to reach the extremes of heat and cold in England, in the latitude of nearly 52° N.^[98a]

Notwithstanding the extremes of heat and cold, which thus appear in the climate of Pennsylvania, Mr. Jefferson remarks (in his Notes on Virginia,) that these extremes are greater at Paris than at Williamsburg, the hottest part of Virginia. Yet Williamsburg, which is only about 2¾° to the southward of Philadelphia, is nearly 11¾° further south than Paris.